1. Field of the Invention
The present invention relates to an electric centrifugal fan used for air blowing.
2. Description of the Related Art
Conventionally, there have been two types of blower fans: axial fans and centrifugal fans. In general, the axial fans are excellent in air flow quantity characteristic, whereas the centrifugal fans are excellent in static pressure characteristic.
For the purpose of cooling an electronic device, such as a notebook computer, in which electronic components are densely packed, excellence in the static pressure characteristic tends to be demanded more than excellence in the air flow quantity characteristic. In particular, the centrifugal fan is commonly adopted for a small-sized blower fan used to cool the notebook computer.
The centrifugal fan includes an impeller portion arranged inside a housing thereof. The impeller portion includes a plurality of blades which are arranged on an outside surface of a covered cylindrical hub forming a portion of a motor. Air is taken in in an axial direction and blown out in a radial direction. The housing of the centrifugal fan typically includes a base, to which the motor is fixed; a side wall defining a flow path of air; and a cover arranged to cover an upper end of the side wall.
In small-sized centrifugal fans, excellence in the static pressure characteristic is often achieved at the sacrifice of the air flow quantity characteristic. Thus, an important technical issue is how to maintain a sufficient air flow quantity.
One conceivable way of maintaining a sufficient air flow quantity is reducing the diameter of the hub to increase air intake. A reduction in the diameter of the hub involves the need to reduce the size of a circuit board arranged below the hub. However, size reduction of electronic components to be mounted on the circuit board has a limit because of technological limitations, and the circuit board arranged below the hub may not have sufficient space for all the electronic components to be mounted thereon. Thus, an issue is how to secure sufficient space for the mounting of all the electronic components.
As such, in some centrifugal fans of a two-side intake type, in which air inlets are defined in both axial sides of the housing, a portion of the base-side air inlet is closed, a portion of the circuit board is arranged to extend over the closed portion, and some of the electronic components are arranged on this portion of the circuit board.
However, regarding the centrifugal fans of the two-side intake type, when a portion of the circuit board is arranged to extend radially outward of the area below the hub to overlap with a wind tunnel, this portion of the circuit board tends to present an obstacle in the flow path of air. Meanwhile, in the case of small-sized centrifugal fans of a one-side intake type, in which electronic components are arranged on an upper surface of that portion of the circuit board which is arranged axially opposite the impeller portion, the electronic components may have such a great axial height as to provide resistance against the flow of air, because of the small size of the centrifugal fans.